It was not until after the Battle of the Boyne (1 July 1690), and during the Siege of Limerick, that Sarsfield became prominent as a leader. He captured a convoy of military stores and artillery at Ballyneety, near Pallasgreen between Limerick and Tipperary, in a raid apparently guided by a rapparee known as 'Galloping Hogan'. This delayed the siege of the town until the winter rains forced the English to retire.
This achievement was said by the Duke of Berwick to have turned Sarsfield's head and made him the popular hero of the war with the Irish. His generosity, his courage and his commanding height, had already commended him to the affection of the Irish. When the cause of King James was ruined in Ireland, Sarsfield arranged the Treaty of Limerick and sailed to France on 22 December 1691, with many of his countrymen who entered the French service in what is known as the Flight of the Wild Geese. During that year he was created Earl of Lucan by King James.
Gilbert Burnet, the contemporary historian, records Sarsfield as having told some English officers at Limerick, "As low as we are now, change but kings with us and we will fight it over again with you", as much in disgust with James' inaction as in admiration of William's generalship.
He received a commission as lieutenant-general (marechal-de-camp) from King Louis XIV and fought with distinction in Flanders until he was mortally wounded at the Battle of Landen, on 19 August 1693. He died two or three days after the battle, aged 33, at Huy, Belgium, where he is buried in the grounds of St Martin's Church. A plaque on the wall of this church marks the approximate location of his grave. He was quoted as watching his lifeblood ebbing away, and saying "Oh, if only this were for Ireland".
He married Lady Honora Burke (or de Burgh), daughter of John Burke, 9th Earl of Clanricarde, by whom he had one son, James Sarsfield, 2nd Earl of Lucan, who died childless in 1718. They also had one daughter, who married Theodor von Neuhoff. His widow remarried to the Duke of Berwick. Patrick Sarsfield's great nephew, Charles Bingham had the title, Earl of Lucan, re-created in 1795.